JPS6118989Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an injection molding machine having a feature in a mixing mechanism section provided in a screw.

In an injection molding machine, the screw moves backward during plasticization and moves forward during injection, so the effective length of the screw changes and the mechanical energy and heat transfer energy applied to the resin change. As a result, the resin temperature changes to a certain extent. The difference is unavoidable.

As a conventional example of the screw, there is a screw for PVC as shown in FIG. 1, but this screw has the disadvantage that there is a large difference in resin temperature before and after the stroke. In addition, in order to reduce the temperature difference, a kneading head section is installed that suppresses heat generation and transfers it to the tip of the screw, where it melts rapidly.
Specific examples include homomelt screws as shown in Figure 2, high-mix screws as shown in Figures 3 to 6, high-mix screws as shown in Figures 7 to 11, There is a Dalmage screw as shown in Figure 11.

Of the various screws mentioned above, Figures 3 to 6
All screws, except for the high-mix screw shown in the figure and the dalmage screw shown in Figure 11, are equipped with a barrier (weir) to create a backflow when the screw rotates to give it a kneading effect, and the resin temperature before and after the stroke changes. Although the difference has decreased, there are still drawbacks such as a decrease in plasticizing ability and insufficient rise in resin temperature.

The present invention is an invention to solve the above-mentioned difficulties, and includes a plurality of notch slopes on the plasticizing side and a plurality of notch slopes on the injection side on the circumferential surface of the mixing part provided at the tip of the screw. are arranged at intervals from each other, and each of the plasticizing side notch slopes and the cylinder inner wall surface creates a plurality of wedge-shaped plasticizing side spaces that become shallower toward the torpedo side, and each of the injection side notch slopes and the cylinder. The mixing mechanism is characterized by a plurality of reverse wedge-shaped injection side spaces that become deeper toward the torpedo side due to the inner wall surface,
An object of the present invention is to provide an injection molding machine which has significantly improved plasticizing performance and injection pressure backup performance.

In the present invention, a plurality of notch slopes on the plasticizing side and a plurality of slopes on the injection side are arranged at intervals on the circumferential surface of the mixing part provided at the tip of the screw as described above. , a plurality of wedge-shaped plasticizing side spaces which become shallower toward the torpedo side due to the above-mentioned respective plasticizing side notch slopes and the cylinder inner wall surface, and which become deeper toward the torpedo side due to the respective injection side notch slopes and the cylinder inner wall surface. Since multiple reverse wedge-shaped injection spaces are provided, during plasticization,
Unmelted resin is trapped by the plurality of wedge-shaped plasticizing side spaces and rapidly melted by strong shearing stress, and the shearing force is further strengthened by the wedge shape with the tip side becoming smaller, resulting in a kneading action and a cleaning action. The injection pressure is significantly increased and stagnation is prevented, and during injection, the injection pressure is backed up by the plurality of oppositely directed wedge-shaped injection side spaces, thereby significantly improving resin plasticization and injection performance.

Embodiments of the present invention are shown in FIGS. 12 to 15 below.
This will be explained using figures.

In the figure, 1 is a screw, and a mixing section 3 is provided at the tip of the screw 1, that is, in front of the torpedo 2, and the mixing section 3 is formed to have a length equivalent to 1 to 3 times the screw diameter. There is.

Further, on the peripheral surface 9 of the mixing section 3, as shown in FIGS. 12 to 15, a plurality of plasticizing side notch slopes 4 (on the right side in the figure) and a plurality of injection side notch slopes 5 are provided at intervals. Each plasticizing side notch slope 4 is formed shallower toward the torpedo 2 side, and each injection side notch slope 5 is formed deeper toward the torpedo 2 side. The slope 4 and the cylinder inner wall surface 6 form a plurality of wedge-shaped plasticizing side spaces 7 (see FIG. 15) that become shallower toward the torpedo 2 side, and the injection side notch slopes 5 and the cylinder inner wall surface 6 form a plurality of wedge-shaped plasticizing side spaces 7 on the torpedo 2 side. A plurality of reverse wedge-shaped plasticization side spaces 8 (15th
(see figure), each wedge-shaped plasticizing side space 7 and each reverse wedge-shaped plasticizing side space 8.
are spaced apart from each other as shown in the figure through the circumferential surface 9 of the mixing portion 3, and are arranged such that the leading end and the trailing end are intersected alternately.

Prior to explaining the operation of the embodiment shown in FIGS. 12 to 15, we will explain the melting process in the phase transition zone (transition zone from solid phase to liquid phase) of the resin in the conventional screw tube having a recess 11 formed on its outer periphery. Figure 16,
To explain with reference to FIG. 17, the solid bed 13 in the screw recess 11 is in contact with the wall portion 12 which faces the screw recess 11 and moves relatively through the molten film 14, and is opposite to the moving side of the recess 11 with respect to the wall portion 12. A melt pool 15 is formed in the side recess 11, but as the melting progresses, the solid bed 13 is crushed, and as shown in FIG. 17, unmelted pellets 17 are suspended in the melt 16. The situation is as follows. In this state, the shearing force due to the rotation of the screw acts on the melt 16 and raises its temperature, but the effect on the unmolten pellets 17 is small. Most of the unmelted pellets 17 are melted by heat transfer energy, resulting in poor melting efficiency.

Considering the above theoretically, the energy received when the resin melts is the heat transfer energy from the cylinder heater (not shown) and the shear energy due to the rotation of the screw, and the shear energy is calculated by the following formula.

The shear rate γ on the wall surface is, when the screw diameter D, the screw rotation speed N, and the groove depth h, γ=πDN/h …(1) The energy P consumed per unit volume is the shear stress Then, P=τγ …………(2) The flow equation for Newtonian fluid is, if the viscosity is μ, τ=μγ …………(3) Substituting equation (3) into equation (2), P=μγ ² = μ [πDN/h] ² ………(4) Therefore, the energy per unit volume due to shearing P
is inversely proportional to the square of the groove depth.

Figures 2, 7 and 8, 9 and 10
As shown in FIG. 21, the mixing head shown in FIG. Therefore, the shear force is small and depends on heat transfer energy, so the melting efficiency is poor.

Further, the cleaning action of the cylinder wall surface and screw surface depends on the shearing force on the surface, and the shearing force has the following relationship. Substituting equation (1) into equation (2), τ=π・D・N・μ/h……(5) Therefore, in the mixing head shown in Figs. 9 and 10, when the groove is cut, Since the groove depth h at the location and the cut end location is large, the cleaning action is small and therefore stagnation occurs at both locations.

However, in the embodiment of the present invention shown in FIGS. 12 to 15, the rotation of the screw transports the molten material and unmelted pellets to the wedge-shaped plasticizing side space 7 that is closed to the tip of the screw, and as shown in FIGS. As shown in Fig. 19, the unmolten pellets are drawn in by the relative movement between the notch slope 4 on the plasticizing side and the cylinder inner wall surface 6 (the plasticizing side notch slope 4 rotates, and the cylinder inner wall surface 6 stops). They are gathered on the circumferential surface 9 of the mixing section 3, which is a corner section. As shown in FIG. 18, the assembled unmelted pellets 18 are strongly pressed against the cylinder inner wall surface 6 by the wedge action of the notch slope 4 on the plasticizing side.

At this time, in the wedge-shaped plasticization side space 7, the 16th
A molten film layer 19 is formed in the same manner as the molten film 14 of the molten model shown in the figure, and the mechanical energy generated by the rotation of the screw becomes strong shear energy that acts on the unmolten pellets 18, rapidly accelerating their melting.

To explain this in more detail, the wedge-shaped plasticizing side space 7 forms a wedge in which the gap between the plasticizing side notch slope 4 and the cylinder inner wall surface 6 becomes smaller as it advances toward the torpedo side, that is, the tip. The unmelted pellets 18 are blocked by the cylinder inner wall surface 6 and the circumferential surface 9 of the mixing section, and are pressed against the cylinder inner wall surface 6, and the molten film layer 1 increases toward the tip.
The thickness h of the mixing head 9 becomes smaller, and the amount of heat generated at the mixing head portion P becomes significantly larger because it is inversely proportional to the square of h, as shown by equation (4), and melting is dramatically promoted.

Furthermore, as the boundary between the wedge-shaped plasticization side space 7 and the opposite wedge-shaped injection side space 8 is approached, the gap h between the plasticization side notch slope 4 and the cylinder inner wall surface 6 becomes smaller and approaches zero, so that equation (5) can be expressed as follows. As can be seen, the shearing force τ becomes extremely large and the cleaning action increases dramatically, so that the grooves start and end as seen in the mixing head shown in FIGS. 9 and 10. There will be no more stagnation.

Further, the melted resin 20 is applied to the mixing part peripheral surface 9.
It passes through the gap between the cylinder inner wall surface 6 and flows into the reverse wedge-shaped injection side space 8, where it is pooled at the tip of the screw.

A certain amount of pooled molten resin is injected into a mold (not shown) in the next cycle, but since the pressure at the tip of the screw is extremely high, the molten resin is injected around the mixing part as shown in Figure 20. Although the flow attempts to flow backward through the gap between the surface 9 and the cylinder inner wall surface 6, the injection pressure is backed up due to the viscosity of the resin itself because the reverse wedge-shaped injection side space 8 is tapered in the reverse flow direction. do. This effect is particularly great for vinyl chloride resins that exhibit plug-flow behavior.

Further, crystalline resins such as polyethylene and polypropylene have a large latent heat of fusion, and unmolten pellets are observed floating in the molten resin. However, in the above embodiment, since the plasticizing side notch slope 4 of the wedge-shaped plasticizing side space 7 moves, the molten resin generates a circulation flow as shown by the arrow in FIG. 18 also flows in the direction of the arrow, but because it tapers along the flow direction,
The unmelted pellets 18 are reliably melted by the large amount of heat generated by the large amount of heat captured at the circumferential surface 9, that is, the corner, and heated to a high temperature by the narrow gap between the plasticizing side notch slope 4 and the cylinder inner wall surface 6. Ru.

In the embodiment described above, the mixing section 3 is provided near the tip of the screw 1, but its installation position can also be moved to the screw side.

[Brief explanation of the drawing]

Figure 1 is a side view of a conventional PVC screw, Figure 2 is a partially longitudinal side view of the lower half of a conventional homomelt screw, and Figure 3 is a side view of a conventional high-mix screw. Figures 4 to 6 are
Fig. 7 is a side view of another conventional screw; Fig. 8 is a cross-sectional view taken along the - line in Fig. 7; 9 is a side view of another conventional screw, FIG. 10 is a cross-sectional view taken along the line - in FIG. 9, FIG. 11 is a side view of still another conventional screw, and FIG. FIG. 13 is a front view of FIG. 12, FIG. 14 is a cross-sectional front view taken along the line - in FIG. 12, and FIG. 15 is an enlarged perspective view of the main parts. Fig. 16 and Fig. 17 are explanatory diagrams illustrating the melting process in the phase transition zone of the resin, Fig. 18 is a cross-sectional explanatory diagram showing the melting process of the embodiment of the present invention, and Fig. 19 is a development of Fig. 18. Figure 20 is a longitudinal cross-sectional side view of Figure 18, and Figure 2
FIG. 1 is a cross-sectional explanatory diagram showing the flow of resin in a conventional method. 1... Screw, 2... Torpedo, 3... Mixing section, 4... Plasticizing side notch slope, 5...
Injection side notch slope, 6...Cylinder inner wall surface, 7...
...Wedge-shaped plasticization side space, 8 reverse wedge-shaped injection side spaces,
9...Surrounding surface (mixing section).

Claims (1)

[Scope of utility model registration request] An injection molding machine characterized by a mixing mechanism section in which a plurality of plasticization side cutout inclined surfaces and a plurality of injection side cutout inclined surfaces are arranged at intervals on the peripheral surface of a mixing section provided at the tip of a screw, and a plurality of wedge-shaped plasticization side spaces which become shallower toward the torpedo side by each of the plasticization side cutout inclined surfaces and the cylinder inner wall surface, and a plurality of inverted wedge-shaped injection side spaces which become deeper toward the torpedo side by each of the injection side cutout inclined surfaces and the cylinder inner wall surface are provided.